A common method of cooling the internal combustion engine of a motor vehicle consists in causing a coolant fluid, such as water or an aqueous solution of an antifreeze preparation, to flow between the engine and a heat exchanger so that the engine yields heat to the fluid, which then yields the heat in the heat exchanger to an external environment, which is generally a stream of atmospheric air.
It is usual to maintain the fluid under pressure, so that it remains in practice in the liquid state regardless of the power level at which the engine is operating, and therefore regardless also of the rate of transfer of the heat to be evacuated from the system. Circulation of the fluid is provided by means of a pump which is driven mechanically by the engine of the vehicle. The output of the pump is therefore proportional to the speed at which the engine is operating. At high engine speeds, the circulating pump works at a high mechanical power which may reach 1 or 2 kilowatts. In addition, the relative pressure of the fluid reaches about 0.8 to 1.2 bar, which makes it more difficult to obtain lasting sealing of the cooling circuit.